Hi Elma,
Make sure your Microsoft account is fully verified at account.microsoft.com/security. Or try using a different browser or open the page in private/incognito mode. You can also clear your cache and cookies, then reload the Rewards page. And confirm your account region matches the reward region (Brazil in this case).
If the button is still disabled after these steps, it may be a system issue. You can contact Microsoft Rewards Support here: https://rewards.bing.com/support. For Xbox-related redemption help, check Xbox Support – Digital Code Solution.